1. Field of the Invention
The present invention relates to the copying of data that resides in direct access storage devices (xe2x80x9cDASDsxe2x80x9d). More particularly, the invention concerns an automated, fault-tolerant method of creating a backup copy of a source DASD volume by first performing an instant virtual copy with source volume identifier (ID) suspended, then creating a non-virtual (physical) backup copy from the instant virtual copy with the source volume ID reintroduced.
2. Description of the Related Art
A number of DASD subsystems are capable of performing xe2x80x9cinstant virtual copyxe2x80x9d operations, also referred to as xe2x80x9cfast replicate functions.xe2x80x9d Instant virtual copy operations work by modifying metadata such as relationship tables or pointers to treat a source data object as both the original and copy. In response to a host""s copy request, the storage subsystem immediately reports creation of the copy without having made any physical copy of the data. Only a xe2x80x9cvirtualxe2x80x9d copy has been created, and the absence of any physical copy is completely unknown to the host.
Later, when the storage system receives updates to the original or copy, the updates are stored separately and cross-referenced to the updated data object only. At this point, the original and copy data objects begin to diverge. The initial benefit is that the virtual copy occurs almost instantaneously, completing much faster than a normal physical copy operation. This frees the host and storage subsystem to perform other tasks. The host or storage subsystem may even proceed to create an actual, physical copy of the original data object during background processing, or at another time.
With such benefits, instant virtual copy has been an important development in modern
DASD subsystems, and a number of different embodiments have surfaced. As one example, International Business Machines Corporation (xe2x80x9cIBMxe2x80x9d) has developed the xe2x80x9cFLASHCOPYxe2x80x9d technique, as described in U.S. application Ser. No. 09/347,344, filed on Jul. 2, 1999 and entitled xe2x80x9cMethod, System, and Program for Maintaining Electronic Data as of a Point-In-Time.xe2x80x9d A different example is the xe2x80x9cSNAPSHOTxe2x80x9d technique disclosed in U.S. Pat. No. 5,410,667 entitled xe2x80x9cData Record Copy System for a Disk Drive Array Data Storage Subsystem,xe2x80x9d which issued on Apr. 25, 1995. The foregoing references are hereby incorporated herein by reference.
The instant virtual copy technique was developed, at least in part, to quickly create a duplicate copy of data without interrupting or slowing foreground processes. A natural extension of this function has been the creation of a non-virtual xe2x80x9cbackupxe2x80x9d copy of the source data, to aid in disaster recovery. Under, one such technique, an operation such as xe2x80x9cFLASHCOPYxe2x80x9d or xe2x80x9cSNAPSHOTxe2x80x9d operation is used to perform an instant virtual copy operation; this creates a virtual target volume identical to the source volume in all respects, even including the volume ID of the source volume. Then, the target volume is taken off-line, which may occur automatically as a result of the instant virtual copy operation or manually at the direction of a system administrator. This is necessary because most systems do not allow multiple volumes with the same volume ID, in order to prevent confusion in uniquely identifying each data volume. After being taken off-line, the (virtual) target volume is used as a source to create a physical backup copy on tape. This may be achieved, for example, using an operation such as a BACKUP, DUMP, etc.
Although the foregoing technique is useful in some respects, there are still certain limitations. Namely, if the system fails prior to taking the (virtual) target volume off-line, confusion can result when the system is brought on-line because there will be two volumes with the same volume ID. Furthermore, if the source volume received any updates prior to system failure, there is a danger of losing these updates if the target volume is incorrectly taken to be the source volume.
A different approach has been developed to avoid the confusion of having both source and target volumes with the same volume ID. In this approach, an operator manually issues an instant virtual copy command with an associated command parameter that causes the system to create a target volume (instant) with a volume ID that differs from its source volume counterpart. This may be achieved, for example, using a xe2x80x9cFLASHCOPYxe2x80x9d command including a xe2x80x9cNO VOLIDxe2x80x9d parameter. This creates an instant virtual copy of the source volume, but with a different volume ID. Next, the operator manually issues another command causing the storage system to create a physical backup copy of the xe2x80x9ctargetxe2x80x9d instant virtual copy. This may be achieved, for example, by using a appropriate command such as BACKUP, DUMP, etc. This creates a non-virtual (physical) backup volume that is identical to the source volume, except for having a different volume ID.
This presents some difficulties if the source volume fails and the backup volume is needed to restore the contents of the source. Namely, since the backup volume""s volume ID does not match that of the failed source volume, a recovered backup volume would not be accessible to applications that expect the volume ID of the failed source volume, and the intended function of the restore operation would be defeated. Consequently, restoration of the backup volume requires the operator to perform the added manual operation of changing the recovered volume""s volume ID to match that of the failed source volume. This may be done, for example, using the ICKDSF utility provided by the IBM DFSMShsm product. Alternatively, the backup volume""s ID may be changed first, and then the volume restoration completed.
Although the foregoing technique is useful in some respects, there are still certain limitations. For one, success of this process requires certain operator input to occur at certain times. As with any process involving humans, the process incurs some risk of error merely because of the human factor. In addition, there are greater labor costs because of the need for human involvement rather than utilizing automated processes. Furthermore, the marketplace demands increasingly competitive, automated solutions to problems such as these.
For the foregoing reasons, then, known backup processes based on the instant virtual copy are not completely adequate for some applications due to certain unsolved problems.
Broadly, the present invention concerns an automated, fault-tolerant method of creating a physical backup copy of a source DASD volume by first performing an instant virtual copy with source volume ID suspended, then creating a non-virtual (physical) backup copy from the instant virtual copy with the source volume ID reintroduced.
According to the invention, the instant virtual copy may be performed using similar principles as a FLASHCOPY operation with the NO COPY VOLID option selected. This creates a virtual duplicate of the source volume on the DASD, minus the source""s volume ID. Advantageously, novel operations are added to provide the virtual target volume with a hidden representation of the source volume ID. Next, the target volume is used as source for a physical copy operation to magnetic tape or other backup media. Importantly, this copy operation utilizes the hidden representation of the source volume ID to reintroduce the source""s volume ID into the backup copy. The resultant backup copy on tape is an exact duplicate of the source volume. After completing the physical backup copy, the instant virtual copy is deleted by freeing data storage allotted to the instant virtual copy for use in other storage purposes. In the case of Home Area Architecture systems, deletion of the instant virtual copy may, for example, be performed using a WITHDRAW FLASH COPY RELATIONSHIP operation.
The foregoing features may be implemented in a number of different forms. For example, the invention may be implemented to provide a method of automated backup using a volume ID-suppressed instant virtual copy followed by a volume ID-reintroducing physical backup copy. In another embodiment, the invention may be implemented to provide an apparatus such as data storage subsystem programmed to perform the automated backup described herein. In still another embodiment, the invention may be implemented to provide a signal-bearing medium tangibly embodying a program of machine-readable instructions executable by a digital data processing apparatus to perform the automated backup copy described herein. Another embodiment concerns logic circuitry having multiple interconnected electrically conductive elements configured to perform the automated backup operations described herein.
The invention affords its users with a number of distinct advantages. For example, the backup operation of this invention minimally impacts the availability of the source volume because the source volume is initially copied using an instant virtual copy technique. As another advantage, the invention encourages fault tolerance because the source volume""s ID is withheld from the target copy, and another volume ID is used instead. Thus, if the subsystem fails just after creating the target copy, the target copy is not likely to be confused with the source copy because they have different volume IDs. Moreover, the resultant tape backup copy is less costly and error prone because it is created by a machine-automated process rather than various commands issued by a system administrator. The invention also provides a number of other advantages and benefits, which should be apparent from the following description of the invention.